B652 Modifications- Upgrades?

[steveeboy]

Re: B652 Modifications- Upgrades?

I had a bad woofer in a 652 so I bought some buyout woofers from PE and threw them in there. They were the GRS 9s PE had on close out back in Spring.

I also did the Zaph mods too (xover, bracing, polyfill, and upgraded internal wiring with heavier gauge speaker wire)...

I asked on here for some tweaks to the Xover based on the GRS9 specs. You can search for that, the experts here just gave me some adjusted values for the woofer.

I think the upgraded woofer did sound better, but as others suggest it is not cost effective unless you get a steal on the new parts. Since my b652s were bad and PE sent me a new pair, I considered the woofer upgrade "cheap" since it was being done to a "Free" pair of b-652s.

Currently, I am running the b-652s with a passive old optimus passive subwoofer powered with a Sure tda7498 amp and it sounds great on my desk. I think the b652s are fun to mod if you just want to get into it. And PE has great customer service and the people on this forum are very helpful.

[Whitneyville1]

Re: B652 Modifications- Upgrades?

For ~ $12 worth of XO parts and some "sweat equity" in modding the enclosures I have learned a lot of what's "worthwhile" and "what you gain" from this laboratory of a pair of off the shelf speakers. I considered changing drivers "cheating" for me. Using the B652's tweeter and an MCM mid-woofer ( a 5 1/4" would work), for ~$40-45 a pair, I'm pretty darn sure I can build a better speaker, if using one of the B652's drivers was a requirement. It surprised me what I learned from a pair of $33 speakers.

[steveeboy]

Re: B652 Modifications- Upgrades?

SO,

I finally got a chance to do an A/B comparison with three sets of B652s all modified with bracing and polyfill as suggested by Zaph. Also replaced internal wiring with 16g speaker cable.

1. Straight Zaph Crossover design

2. b652 with GRS 8 ohm woofer upgrade and a slightly modified Zaph crossover with some ideas from the "cabrini" project found on here-johnny richards design. For woofer there I used a 1mH coil with a 6uF + 10ohm shunt circuit with tweeter circuit same as original Zaph

3. A Dennis Murphy designed crossover for which he was kind enough to send me the schematics. That one is .8 mH coil in series with woofer with 3ohm resistor and 12uF cap paralleled across leads. And 10UF cap in series with tweeter,then 2 ohm resistor and .33mH coil parallel across leads AND 1 ohm resistor in series with tweeter. I used the more expensive Dayton polypropylene capacitors for the tweeter in these.


Prior to this test, I had only used the modified speakers as part as my desktop near field set up. I power them there with a SURE tda7498 amp and run them with an optimus passive subwoofer.

For the test, I set the modified b652s up on a yamaha 773 AVR feeding a vintage Sansui b2101 power amp as" set a" and "set b" and switched back and forth. I compared all three sets to each other and picked the best sounding ones for each round.

I used a FLAC files of Pink Floyd "Dark Side of the Moon."


I was astonished at how much power was needed to get any kind of volume out of the b652s. I would never be able to play the Sansui amp at that high a level with my main speakers--Cerwin-Vega PD-9s. I mean the neighbors would call the cops for sure. Crazy how inefficient the b652s are compared to the CVs. Crazy too how little bass there is from these bookshelves at any volume. I guess the sub under my desk REALLY helps them out.

Of the three modded b652s, the Dennis Murphy crossover one had the best sound. They sounded the best during the test and they also sound the best in my near field desk set up. They had the nicest high end and mid range. The Zaph crossover set with original drivers was second. bass was not really that different from the straight Zaph modified speaker set, but the way the high end sounded just didn't seem as "shimmery" or clear. The B652s with the new woofers were a distant third for sure. The set with the GRS 8 ohm woofers aren't "right" with that slightly modified Zaph crossover. They just sounded weak. I am going to replace the GRS woofers with some of the PE original 4 ohm woofers and run a straight zaph crossover there.

I do think the tweaks are worthwhile, and I want to let people know that with the new sets of b652s, to my ear the Dennis Murphy crossover sounds better than the Zaph one.

So, while I really appreciate all that I have learned working with these B652s, I think I am pretty much at the end of my tweaks.

[Pete Basel]

Re: B652 Modifications- Upgrades?

Nice work comparing the different mods. I wasn't sure if I was following your description of the Dennis Murphy mod, is this correct below: Are the drivers wired in phase?
EDIT: SCHEMATIC WAS WRONG - SEE LATER POST #22 FOR CORRECTION

[Whitneyville1]

Re: B652 Modifications- Upgrades?

On "projects" like these, you've got to know when to say "good 'nuff" and quit throwing money at them. J. Richards has cooked up several bookshelf speakers in the "bargain basement" price range using MCM drivers. Minus cabinets and such, better sounding speakers can be built for about $65 a pair. I'm assuming you have a saber-saw, electric drill (cordless is better) and some (bunch) of clamps.A router is a BIG bonus, but a "scrolling" (free-head) saber-saw and the narrow scrolling blades will do a 4" diameter cut-out. A "no-name" or reconditioned "Roto-Zip" type tool (get a heavier duty one than the 1.1 amp Dremel). You can buy surface mount drivers. While not "ideal", many very good designs have been built with them. Double the money, many, many times the performance.

[steveeboy]

Re: B652 Modifications- Upgrades?

Nice work comparing the different mods. I wasn't sure if I was following your description of the Dennis Murphy mod, is this correct below: Are the drivers wired in phase?

Pete,

you have the woofer correct.

According to the schematic Dennis Murphy was kind enough to send me, the tweeter circuit is slightly different.

You have it cap, then 2 ohm resistor, then the 1 ohm resistor and inductor paralleled from that point.

Dennis Murphy had the cap and then the two resistors paralleled from it--the 1 ohm connected to the + pole of tweeter, and the 2 ohm connected to the .330mH inductor.

The phase is not inverted.

[Pete Basel]

Re: B652 Modifications- Upgrades?

Thanks, so I think this is correct now: